Incidence of hyperprolactinemia in patients with Hashimoto's thyroiditis.

The causes of hyperprolactinemia, the correlation between serum levels of PRL and thyroid function and magnetic resonance imaging (MRI) of the pituitary were studied in patients with chronic thyroiditis. Seventy-four female patients and 15 normal control women participated in this clinical survey. Fourteen of 74 patients with various thyroid conditions had increased serum PRL. The incidence of hyperprolactinemia in the overt primary hypothyroid group was 42.4% and was significantly higher than in any other group with normal serum thyroxine. There was a close association between the increment in serum PRL and of free triiodothyronine above the basal level after TRH administration. There were 14 patients with hyperprolactinemia in three of which serum PRL was over 60 micrograms/L. PRL producing tumor, severe primary hypothyroidism and liver cirrhosis were detected in these three patients, respectively. These results indicate that the pathogenesis of increased serum PRL was not uniform in patients with Hashimoto's thyroiditis, although there was a correlation between hyperprolactinemia and impaired thyroid function. It is proposed, therefore, to measure and follow serum levels of PRL and MRI of the pituitary in patients with chronic thyroiditis, especially with impaired thyroid function.